Proposal
This paper presents the results of a study of processes and technologies for the thermal desorption of oil from oil-based drilling fluids cuttings for both onshore and offshore applications. A field investigation of available technologies designed to separate oil from oil-based drilling fluids cuttings by thermal desorption was conducted. In addition, some technologies that perform separation by physical-chemical means were also investigated; however, all commercial processes presently available use thermal desorption.
The mechanisms of desorption of oil from cuttings were investigated. Process parameters and theoretical concepts for thermal desorption by distillation were developed using proprietary computer simulation programs for the distillation of hydrocarbons. Theoretically ideal temperatures for the process were calculated for various conditions and for various oils. The impact of moisture and oil content on the heat balance was calculated. The recoverability of the oil under various conditions was investigated.
Nineteen companies were contacted for information on their desorption technology. Twelve company sites were visited to determine the developmental stage of their technology and to determine how well the technology functioned in the field. The technologies were evaluated for air emissions, liquid emissions, safety, oil content of processed material, space requirements, utility and chemical requirements, and other operating and design factors. Applicability of the technologies for offshore use was evaluated. Safety and environmental issues for each technology and the recycling of oil are also addressed in this paper, along with future work needs in this area.
Introduction
The need for thermal desorption of oil from drilling cuttings for environmentally acceptable disposal of the cuttings was identified in the early 1990s. Technologies used for this purpose evolved significantly in the intervening years. The requirements for the level of oil removal have also evolved. The numbers of base fluids used in the drilling fluids have increased beyond diesel and mineral oils to a wide range of synthetic fluids that include, but are not limited to, alkanes, olefins, esters, and blends thereof. For the purposes of this paper, the term "oil" covers all such base fluids used in continuous phase of invert emulsion drilling fluids.
The requirements of desorption technology differ significantly depending on three main factors:where the operations take place,the Total Petroleum Hydrocarbons (TPH) levels permitted to remain on the cuttings, andthe protocols for TPH measurement.
The authors investigated 16 different desorption technologies in various stages of development from bench-scale units to pilot-plant stage to commercially available units. The focus was primarily on thermal units because these were the only types commercially available at this time.
In Europe and South America, the processed cuttings typically measure less than 1% by weight of TPH before disposal in landfills. For offshore disposal of cuttings in the UK sector of the North Sea, an oil content of less than 1% is also required, and any discharged water must have less than 40 parts per million (ppm) of oil. Generally, oil-based cuttings generated offshore in the North Sea have been taken to land for treatment and disposal because, until recently, no method for reducing the oil content to less than 1% was available at an offshore location.
Regulatory agencies in other areas have also set standards for the levels of TPH in cuttings whether disposed of offshore or on land. Some processes do not require thermal desorption technologies. For example, in the Gulf of Mexico the discharge of cuttings with TPH levels of either 6.9% or 9.4% by weight, depending on the synthetic oil selected, is allowed if other toxicity and biodegradation standards are met or exceeded. These levels of oil on cuttings can be reached with mechanical systems. However, the trend in environmental regulations is toward greater stringency. An increased demand for minimal TPH levels in treated cuttings will drive the development of more effective oil-removal technologies.
